The present invention relates generally to a walk-behind working machine including a drive source for producing a motive power, traveling portions, and a power transmission system for transmitting the motive power to the traveling portions so as to propel the machine, and in particular to an improvement in a clutch of the power transmission system.
Walk-behind working machines include tillers, carts, and snow removing machines. Such working machines have drive sources for producing motive powers and are propelled by the motive powers. During propulsion of the working machine, operators walk behind and steer the working machines, holding operational handles of the machines. The machines also have traveling portions such as wheels and endless belts, and power transmission systems for transmitting the motive powers to the traveling portions. The power transmission systems include clutches. Operation of the clutches enables the machines to travel straight or make turns.
The walk-behind working machines are known from, for example, Japanese Utility Model Post-Exam Publication No. SHO 49-21844 entitled xe2x80x9cTURNING DEVICE FOR MOVABLE AGRICULTURAL MACHINExe2x80x9d and Japanese Utility Model Post-Exam Publication No. HEI 7-9742 xe2x80x9cCLUTCH MECHANISMxe2x80x9d.
The publication No. SHO 49-21844 discloses a walk-behind movable agricultural machine including dog clutches. The publication No. HEI 7-9742 discloses a walk-behind movable agricultural machine including a ball-type clutch as will be explained with reference to FIG. 9. The walk-behind machines as disclosed in the above two publications have clutch levers for switching the clutches between engaged and disengaged positions, as will be discussed below in detail.
FIG. 9 hereof shows in cross-section the clutch of the walk-behind working machine 100 of the publication No. HEI-7-9742.
The working machine 100 for doing agricultural work includes an engine (not shown), a transmission mechanism 101, right and left clutch members 103, 103 for turning the machine 100, and right and left axles 104, 104. The transmission mechanism 101 has a driven sprocket 102. The axles 104, 104 are disposed in alignment. Each axle 104 has one end having the sprocket 102 rotationally fitted thereto. The engine produces a motive power to be transmitted via the sprocket 102 and the clutch members 103, 103 to the axles 104, 104.
The axles 104, 104 each have a spline groove 105 formed at the one end thereof. The driven sprocket 102 includes a hub 106 having apertures 107, 107 formed to extend therethrough. The apertures 107, 107 communicate with the grooves 105, 105. The clutch members 103, 103 each have balls 108 and a clutch change member 109 for bringing the balls into and out of the grooves.
The machine 100 includes right and left operational handles positioned at a rear part thereof. The handles have the right and left clutch levers, respectively. Manipulating the clutch levers operates either one or both of the right and left clutch members 103, 103 such that the balls come into and out of the grooves.
More specifically, when an operator grips the right clutch lever, for example, the right clutch member 103 is placed in an OFF state where the balls of the right clutch member 103 come out of the grooves. This makes it possible to transmit the motive power from the engine only to the left axle 104. Therefore, the machine 100 turns right.
When in use, the working machine 100 usually travels on rough or lumpy surfaces. The operator should operate the clutch lever, holding the operational handles and taking into account how much roughness the surface has in order that the machine 100 is turned leaving a desired trail. The operator is required to have a skill or technique high enough to operate the clutch levers and hold the handles in a posture suitable for steering the machine 100. Such operations of the operational handles and the clutch levers of the working machine 100 require greater manpower or effort. To address this problem, the clutch of the working machine 100 needs to be improved. Further, the clutch members 103, 103 and the clutch levers have complicated construction. These problems with the working machine 100 are found in the machine of the publication No. SHO 49-21844 as well.
One may propose to provide a well-known differential gear mechanism between the axles 104, 104, instead of the clutch members 103, 103. The differential gear mechanism is complicated in construction, however. This would lead to increased cost of the working machine 100.
An object of the present invention is to provide a walk-behind working machine including a clutch simply constructed to enable an operator to turn the machine easily.
According to one aspect of the present invention, there is provided a walk-behind working machine comprising: a motive power source for producing a motive power; right and left transmission shafts having outer peripheral surfaces having first grooves formed thereon; and a clutch for transmitting the motive power from the drive source to the right and left transmission shafts; the right and left transmission shafts each having one end, the ends of the right and left transmission shafts having right and left butting surfaces formed thereat, the right and left butting surfaces butting against each other, such that the right and left transmission shafts are disposed in alignment; the clutch including: a cylindrical member rotationally mounted around the ends of the right and left transmission shafts, the cylindrical member having an inner peripheral surface having second grooves formed thereon; and balls each disposed within a space defined by the first groove and the second groove; the cylindrical member capable of rotating to thereby rotate the right and left transmission shafts by means of the balls; the first grooves each having a generally V-shaped configuration and being directed in the direction of rotation of the right and left transmission shafts, the first grooves each having a leading end positioned between the right and left butting surfaces, the first grooves of the generally V-shaped configuration each having a bottom surface and a wall surface continuous with the bottom surface, the bottom surface and the wall surface contacting the ball.
Each first groove of substantially V-shaped configuration includes a pair of half grooves provided on the right and left transmission shafts, respectively. Each half groove has a side surface.
Transmission of the motive power rotates the cylindrical member. Rotation of the cylindrical member causes the transmission shafts to rotate in such a direction as to propel the working machine. The working machine includes a pair of operational handles used for turning the working machine. When the working machine is turned towards either of right and left sides, one of the handles positioned oppositely from the side of the tiller towards which the tiller is to be turned is pushed more strongly than the other handle. This causes the transmission shaft corresponding to the one handle to rotate relative to the transmission shaft corresponding to the other handle. The half groove of the transmission shaft corresponding to the one handle is shifted in the direction of rotation of the transmission shaft. At this moment, the side surface of the half groove of the transmission shaft corresponding to the one handle becomes out of contact with the ball.
Each ball then rolls into the half groove of the transmission shaft corresponding to the one handle. Consequently, the ball pushes only the side surface of the half groove of the transmission shaft corresponding to the one handle. Therefore, the transmission shaft corresponding to the one handle keeps rotating while the transmission shaft corresponding to the other handle stops rotating. This enables the working machine to turn towards the one side.
Turning the working machine readily and rapidly requires only an easy operation of pushing the one handle more strongly than the other handle. In other words, there is no need to provide the working machine with additional clutch levers which would otherwise be operated to turn the working machine. It thus becomes possible to facilitate the operation for turning the working machine. The thus arranged working machine can be propelled straight or turned reliably.
Provision of the clutch made up by the cylindrical member and the balls helps reduce the number of components of the working machine. In addition, the thus arranged working machine is rendered simple in construction. The clutch is cheap to thereby reduce a cost for the working machine.